I think there's still a lot of research to be done in this area, but most of what I've read shows that exercise has minimal impact on this (and on obesity) and

I think there's still a lot of research to be done in this area, but most of what I've read shows that exercise has minimal impact on this (and on obesity) and for both, diet is a far larger contributing factor. That said, it's not even conclusive that diet has been the cause of lower T levels over the years. That's part of why it's so disturbing... we have this huge change in a core part of the biological basis of masculinity at the same time as we're seeing social shifts that seem affected by it (both positive and negative) and minimal research funding seems directed at these questions (although there's been enough research over the years that the preponderance of evidence really strongly points to plastics critically messing with our hormone balances as humans).